Use of coke compositions for on-line gas turbine cleaning

Abstract

A method is disclosed for removing deposits from rotating parts of a gas turbine engine while under full fire or idle speed utilizing a particulate coke composition. The coke composition may be introduced directly into the combustion chamber (combustor) of the gas turbine or, alternatively, anywhere in the fuel stream, water washing system, or the combustion air system. By kinetic impact with the deposits on blades and vanes, the deposits will be dislodged and will thereby restore the gas turbine to rated power output. If introduced into the compressor section, the coke particles impinge on those metal surfaces, cleaning them prior to entering the hot gas section where the process is repeated.

Description

RELATED APPLICATIONS[0001]This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61 / 500,049 filed 22 Jun. 2011 (Jun. 22, 2011).BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]Embodiments of this invention relate generally to gas turbine cleaning methods.[0004]More particularly, embodiment of this invention relate to methods for on-line cleaning of the internal surfaces of selected sections of a hydrocarbon fuel burning gas turbine, which may include compressor sections, hot gas paths, and when present, attendant heat recovery equipment, where the cleaning methods utilize expandable and / or non-expandable coke particles to effect surface cleaning during operation.[0005]2. Description of the Related Art[0006]Gas turbines burning heavy fuels in particular are subject to a rapid buildup of ash deposits on the hot gas path that requires them to be shut down on a regular basis for thorough cleaning by water washing. In these inst...

AI Technical Summary

Benefits of technology

Enables continuous operation and effective removal of ash deposits, reducing power losses and maintenance needs, while being environmentally safe and cost-effective, with the potential for reduced material usage and easier particle capture and reuse.

Problems solved by technology

Gas turbines burning heavy fuels in particular are subject to a rapid buildup of ash deposits on the hot gas path that requires them to be shut down on a regular basis for thorough cleaning by water washing.

These deposits may result in lost power generation for the operator, amounting to potentially hundreds of thousands of dollars per month.

Furthermore, deposits formed on the boiler tubes interfere with normal heat transfer; thereby reducing the quantity of steam produced which is a further drain on operating revenues.

Many users consider heavy, dirty fuels, but regard the increased maintenance and lost power to be more troublesome than it is worth in fuel cost savings.

However, the use of less than clean fuels remains only a minor percentage of fuels for this more important application.

Instead, many gas turbines consume large quantities of natural gas and distillate fuels.

Essentially all gas turbines, regardless of the fuel used, suffer power losses due to ingested contaminants in the large volumes of air required to support combustion.

With time, these contaminants (e.g., dirt, salt spray, fuel residues, etc.) coat the extremely large surface area of the compressor section.

As the deposits accumulate, compressor efficiency is affected and, in addition, the rotational speed of the turbine may be affected.

In the meantime, power output and revenue are lost from the gas turbine operation.

A major problem in gas turbine operation on heavy fuels is the presence of sodium and vanadium in the heavy fuel.

Both are extremely corrosive at the temperatures attained by modern gas turbines.

These deposits hinder the gas flow path streamline flow resulting in reduced power output, decreased efficiency (or increased heat rate), and increased compressor pressure ratio.

Gas turbines in peaking service that are shutdown daily may experience very slow rates of ash deposition.

These deposits are much harder to remove.

As more ash goes through the unit per constant internal surface area, the chances become greater that this ash will build up on the hot gas path parts.

Unfortunately, many of the nutshells end up as extremely fine carbon ash that lacks the energy to clean the deposits.

Also unburned nutshells can end up in bearings and other areas of the gas turbine where they are an unwanted nuisance.

As a consequence of the difficulties of controlling the nutshells, this method of cleaning is used only when necessary.

There are many drawbacks to this method, the foremost being that the turbine is out of service during the entire cleaning operation.

Additionally, the cleaning is often not adequate to completely remove all deposits.

When the gas turbine is placed back into service with deposits still remaining, these deposits can become very hard from being subjected to additional periods of high temperature.

When the deposits are hard enough, it may become necessary to dismantle the gas turbine to laboriously hand clean the deposits from surfaces.

Also Langford places no realistic size limit on these coke particles specifying an upper size of 3.35 mm, clearly too large to be safely used without causing damage to the gas turbine metallurgy.